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排序方式: 共有208条查询结果,搜索用时 15 毫秒
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SOLIMAN A.Y. BAKEER H.M. ATTIA LA.Science Department Faculty of Teachers P.O.Box Alhasa Saudi Arabia Chemistry Department Faculty of Science Fayoum Cairo University EgyptFaculty of Engineering Ain Shames University Egypt 《中国化学》1996,14(6):532-540
3-(4-Phenyl) benzoyl propionic acid was used as the starting material for the synthesisof furanones (2), pyrrolinones (5), pyridazinones (7), benzoxazinones (8) and quinazolinones (9-11). The behaviour of the derivatives of furanones and benzoxazinones toward different nucleophiles is reported. 相似文献
3.
The electrophoretic mobility of three-arm asymmetric star DNA molecules, produced by incorporating a short DNA branch at the midpoint of rigid-rod linear DNA fragments, is investigated in polyacrylamide gels. We determine how long the added branch must be to separate asymmetric star DNA from linear DNA with the same total molecular weight. This work focuses on two different geometric progressions of small DNA molecules. First, branches of increasing length were introduced at the center of a linear DNA fragment of constant length. At a given gel concentration, we find that relatively small branch lengths are enough to cause a detectable reduction in electrophoretic mobility. The second geometric progression starts with a small branch on a linear DNA fragment. As the length of this branch is increased, the DNA backbone length is decreased such that the total molar mass of the molecule remains constant. The branch length was then increased until the asymmetric branched molecule becomes a symmetric three-arm star polymer, allowing the effect of molecular topology on mobility to be studied independent of size effects. DNA molecules with very short branches have a mobility smaller than linear DNA of identical molar mass. The reason for this change in mobility when branching is introduced is not known, however, we explore two possible explanations in this article. (i) The branched DNA could have a greater interaction with the gel than linear DNA, causing it to move slower; (ii) the linear DNA could have modes of motion or access to pores that are unavailable to the branched DNA. 相似文献
4.
MENG Jian REN Yu-Fang LI Xiao-GuangLaboratory of Rare Earth Chemistry Physics Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun Jilin ChinaPopov V.V. Repin S.M. Smirnov LA. loffe Physicotechnical Institute Russian Academy of Sciences Saint Petersburg Russia 《中国化学》1994,12(5):419-424
YBa2Cu3-xVxO7-y(x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) superconductors have been prepared. X-ray diffraction shows that the system remains orthorhombic for all compositions studied, but for x > 0.4 V2O5 was detected as an impurity phase. Substitution of V5+ for Cu2+ occurs in the Cu(2) sites on the Cu(2)-O planes. The introduction of the high valence element, vanadium, produces the extra free-electrons. These electrons recombine with the positive carrier of the system. It makes depression of the mobility and the Hall number of YBa2Cu3-xVxO7-v and also results in a depression of TC. 相似文献
5.
MARIAN ELBANOWSKI MARIA PAETZ JANUSZ SIAWINSKI LESZEK CIELA 《Photochemistry and photobiology》1988,47(3):463-466
Abstract— Chemiluminescence of the Eu(II)/Eu(III)-adenine nucleotide-H2 O2 system and fluorescence of the Eu(III)-adenosine triphosphate system have been investigated. The spectral distribution of the chemiluminescence emission has shown an occurrence of three main bands (Λ=470–480,590–620 and ca. 700 nm). The energy transfer process from the adenosine triphosphate molecules to the Eu(III) ions has been observed in the fluorescence spectrum. The examined chemiluminescence and fluorescence spectra show that these both kinds of emission originate from the 5 D *** τ7 F*** ( n =1–4) transitions in the Eu(III) ions. 相似文献
6.
H. J. Fiedler und N. P. Archer 《Fresenius' Journal of Analytical Chemistry》1967,226(1):114-122
Zusammenfassung Zur schnellen Abtrennung von Caesium aus Spaltprodukten werden zwei Methoden beschrieben, die rubidiumfreie Präparate ergeben: Beim ersten Verfahren wird Caesium zweimal aus schwach saurer Lösung als Tetraphenyloborat gefällt und dann durch Fällung des Caesiumwismutjodids aus Essigsäure vom Rubidium getrennt; beim zweiten, schnelleren Verfahren wird Caesium durch Isotopenaustausch an Caesiumphosphormolybdat in 8 n Salpetersäure isoliert und dann als Wismutjodid gereinigt. Die Anwendung dieser Methoden zum Studium der Nuklide 9,5 min 139Cs, 65 sec 140Cs, 24 sec 141Cs und 18 min 141Ba wird kurz erörtert.
Herrn Prof. Dr. F. Strassmann zum 65. Geburtstag gewidmet.
Wir danken den Herren Prof. F. Strassmann, G. Herrmann und T. J. Kennett für die Förderung dieser Arbeit, dem Bundesministerium für wissenschaftliche Forschung, Bad Godesberg, für finanzielle Unterstützung und der Adolf TodtStiftung für eine Reisebeihilfe (H. J. F.). 相似文献
Summary Two fast separation methods of caesium from fission products are described which yield rubidium-free samples. In the first method caesium is twice precipitated as tetraphenyloborate from weak acid solution and than purified from rubidium by precipitating caesium bismuth iodide from acetic acid solution. In the second, faster method caesium is isolated by isotopic exchange with preformed caesium phosphomolybdate in 8 N nitric acid and than purified as caesium bismuth iodide. The application of these methods in decay scheme studies of 9.5 min 139Cs, 65 sec 140Cs, 24 sec 141Cs and 18 min 141Ba is briefly discussed.
Herrn Prof. Dr. F. Strassmann zum 65. Geburtstag gewidmet.
Wir danken den Herren Prof. F. Strassmann, G. Herrmann und T. J. Kennett für die Förderung dieser Arbeit, dem Bundesministerium für wissenschaftliche Forschung, Bad Godesberg, für finanzielle Unterstützung und der Adolf TodtStiftung für eine Reisebeihilfe (H. J. F.). 相似文献
7.
We have developed a procedure for synthesizing large stable branched DNA structures that enables visualization via fluorescence microscopy. Using this procedure we have synthesized large DNA stars and observed their electrophoretic behavior in polymer solutions and gels. In dilute polyacrylamide solutions, the DNA stars move as random coils and appear to experience only brief collisions with the polymer chains in solution. The effect of polymer solution concentration on the electrophoretic mobility of stars in the dilute regime is found to be in good accord with predictions of the transient entanglement coupling (TEC) model. In semidilute polymer solutions, the star arms extend in the field direction and drag the core through the matrix. The star arms form several U-shaped conformations as they collide and engage with polyacrylamide chains. The U-shaped conformations occasionally evolve into J-shaped conformations as the star arms slide off the matrix chains they engage during electrophoretic migration. In concentrated polymer solutions, the arms of the star extend and form V-shaped structures with the core as the apex. The arms then pull the core through the matrix. These V-shaped conformations are much longer-lived than U-shaped ones and, unlike the latter, do not transform to J-shaped conformations. In polyacrylamide and agarose gels, where matrix entanglements are fixed, DNA stars become trapped when entanglements with matrix molecules prevent the core from being pulled through the matrix by the extended arms. This trapping was observed at all gel concentrations and electric fields studied. 相似文献
8.
Robert M. Archer Dr. Sylvain F. Royer William Mahy Dr. Caroline L. Winn Prof. Michael J. Danson Dr. Steven D. Bull 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(8):2895-2902
Practical syntheses of 2‐keto‐3‐deoxy‐D ‐xylonate (D ‐KDX) and 2‐keto‐3‐deoxy‐L ‐arabinonate (L ‐KDA) that rely on reaction of the anion of ethyl 2‐[(tert‐butyldimethylsilyl)oxy]‐2‐(dimethoxy phosphoryl) acetate with enantiopure glyceraldehyde acetonide, followed by global deprotection of the resultant O‐silyl‐enol esters, have been developed. This has enabled us to confirm that a 2‐keto‐3‐deoxy‐D ‐gluconate aldolase from the archaeon Sulfolobus solfataricus demonstrates good activity for catalysis of the retro‐aldol cleavage of both these enantiomers to afford pyruvate and glycolaldehyde. The stereochemical promiscuity of this aldolase towards these enantiomeric aldol substrates confirms that this organism employs a metabolically promiscuous pathway to catabolise the C5‐sugars D ‐xylose and L ‐arabinose. 相似文献
9.
Qing Zhao Luojia Liu Jiefu Yin Jingxu Zheng Duhan Zhang Prof. Jun Chen Prof. Lynden A. Archer 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(8):3072-3076
Understanding cation (H+, Li+, Na+, Al3+, etc.) intercalation/de-intercalation chemistry in transition metal compounds is crucial for the design of cathode materials in aqueous electrochemical cells. Here we report that orthorhombic vanadium oxides (V2O5) supports highly reversible proton intercalation/de-intercalation reactions in aqueous media, enabling aluminum electrochemical cells with extended cycle life. Empirical analyses using vibrational and x-ray spectroscopy are complemented with theoretical analysis of the electrostatic potential to establish how and why protons intercalate in V2O5 in aqueous media. We show further that cathode coatings composed of cation selective membranes provide a straightforward method for enhancing cathode reversibility by preventing anion cross-over in aqueous electrolytes. Our work sheds light on the design of cation transport requirements for high-energy reversible cathodes in aqueous electrochemical cells. 相似文献
10.